Multi-Dimensional Damage Detection

ABSTRACT

Methods and systems may provide for a structure having a plurality of interconnected panels, wherein each panel has a plurality of detection layers separated from one another by one or more non-detection layers. The plurality of detection layers may form a grid of conductive traces. Additionally, a monitor may be coupled to each grid of conductive traces, wherein the monitor is configured to detect damage to the plurality of interconnected panels in response to an electrical property change with respect to one or more of the conductive traces. In one example, the structure is part of an inflatable space platform such as a spacecraft or habitat.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.13/495,862 filed on Jun. 13, 2012, which claims the benefit of priorityunder 35 U.S.C. §119(e) from U.S. Provisional Patent Application Ser.No. 61/497,631 filed on Jun. 16, 2011, the contents of which areincorporated herein by reference.

ORIGIN OF THE INVENTION

The invention described herein was made in the performance of work undera NASA contract and by employees of the United States Government and issubject to the provisions of Public Law 96-517 (35 U.S.C. §202), and maybe manufactured and used by or for the Government for governmentalpurposes without the payment of any royalties thereon or therefore.

BACKGROUND OF THE INVENTION

1. Technical Field

Embodiments of the invention generally relate to damage detection. Moreparticularly, embodiments relate to the use of a grid of conductivetraces to detect damage to platforms such as inflatable spacecraftstructures, rigid habitation structures, other terrestrial inflatablestructures, and composites.

2. Discussion

Early versions of inflatable structures intended for use in outer spaceand habitation often relied upon the use of thin films to produce thestructure's outer skin. More recently, approaches to creating suchinflatable structures utilize a multilayer approach, with relativelythin layers separated by thicker, more robust layers, providing alayered composite structure with significantly improved damageresistance. Even though such composite structures are more robust, theyare susceptible to penetration damage from micrometeorites and otherspace debris.

During launch and landing operations, plume ejecta can be a significantsource of damaging debris. Currently, the method for determining damageto inflatable structures utilizes differential pressure systems, whichtend to work better if damage causes an actual leak. However, if thedamage is relatively minor, it is more difficult to determine the extentof the damage. Minor damage can lead to more significant damage ifundetected and not addressed as soon as possible.

In an effort to detect such damage, very thin wires or conductive tracesor fibers may be embedded into the composite material. Such systems canbe difficult to fabricate, however, and may not be easy to connecttogether at the system level. The present invention provides new andnovel methods, systems, and apparatus for use in damage detectionapplications.

BRIEF DESCRIPTION OF THE DRAWINGS

The various advantages of the embodiments of the present invention willbecome apparent to one of ordinary skill in the art by reading thefollowing specification and appended claims, and by referencing thefollowing drawings, in which:

FIG. 1A is an illustration of an example of an inflatable spacecraftaccording an embodiment;

FIG. 1B is an exploded view of an example of a layered shell of aninflatable habitat according to an embodiment;

FIG. 2 is a diagram of an example of a detection pattern defined by agrid of conductive traces according to an embodiment;

FIG. 3A is a diagram of an example of a detection system according to anembodiment;

FIG. 3B is an enlarged view of an example of the detection panelassembly shown in FIG. 3A;

FIG. 4 is a sectional view of an example of a plurality of detectionlayers according to an embodiment;

FIG. 5 is a sectional view taken along lines 5-5 of FIG. 3 according toan embodiment;

FIG. 6 is a side view of an example of a flexible detection panelassembly according to an embodiment;

FIG. 7 is a flowchart of an example of a method of evaluating astructure according to an embodiment;

FIG. 8 is a flowchart of an example of a method of detecting damageaccording to an embodiment; and

FIG. 9 is an illustration of an example of a graphical user interface(GUI) according to an embodiment.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments of the present invention may provide a method of detectingdamages to surfaces. For example, the exterior structure of aninflatable space platform such as a spacecraft or habitat located inouter space. Damage caused by impacts of foreign objects, e.g.,micrometeorites, can easily rupture the shell of the inflatable orhabitation structure, causing loss of critical hardware and/or life ofthe crew. While not all impacts will have a catastrophic result, it canbe advantageous to identify and locate areas of the exterior shell thathave been damaged by impact so that repairs (or other provisions) can bemade to reduce the probability of shell rupture and ultimate failure.Embodiments of the present invention involve a system that may providereal-time data regarding the health of the inflatable shell of astructure, specifically including data related to the location and depthof any impact damage. Other embodiments include detecting damage toaircraft, spacecraft, composite materials, and textiles. Still furtherembodiments involve detecting damage to interior surfaces,non-inflatable structures, and other terrestrial inflatable structuressuch as military shelters.

Embodiments of the present invention can also provide amulti-dimensional damage detection system that identifies both theprecise location and extent of damage to an inflatable structure.Incorporated into the embodiments may be related technology of detectingdamage to thin films, including new methods of fabricating and testingnew versions of conductive materials in thin-film layers that may beutilized in external structures, solar arrays, windows, casings, andfabrics.

FIG. 1A illustrates an inflatable spacecraft 10 including an exteriorstructure that may be susceptible to damage from debris during launch,orbit, and/or landing. Accordingly, the exterior structure of thespacecraft 10 may be fabricated from a plurality of interconnectedpanels 12, wherein each panel 12 has a plurality of detection layersseparated from one another by one or more detection layers. As will bediscussed in greater detail, the plurality of detection layers can forma grid of conductive traces that may be monitored for electricalproperty changes. The detection of such electrical property changes canenable advanced damage detection activities such as the generation ofdiagnostic and/or prognostic outputs with respect to the exteriorstructure of the inflatable spacecraft 10. Wherein the outputs canidentify damage to individual panels 12 via a spatially oriented orglobally positioned coordinate system with respect to the inflatablespacecraft 10. Furthermore, the specific damage site locations on saidindividual panels 12 are determined by said panel's grid of conductivetraces. FIG. 1B demonstrates that the outer shell/structure of a spacehabitat may include multiple layers.

FIG. 2 shows a detection pattern 14 that might be defined by amulti-layer grid of conductive traces. Several detection layers can beimplemented, where alternate layers are arranged in an orthogonaldirection with respect to adjacent layers. The orthogonal arrangementallows for pinpointing the exact location of the damage to the surfaceof the structure. Moreover, multiple detection layers allow for thecalculation of the depth of the damage to the surface. Indeed, eachdetection layer may also include multiple known defect traces tofacilitate panel identification as well as damage zone determination, aswill be discussed in greater detail. The illustrated detection pattern14 demonstrates that conductive traces of successive detection layersmay be arranged perpendicular or angled to one another in order toprovide the desired detection grid. For example, a first panel 16 has adetection pattern with a relatively high resolution, wherein a secondpanel 18 and a third panel 20 have a relatively low resolution. Thus,the first panel 16 could be used in areas of an exterior structure thatare particularly susceptible to damage (e.g., sensitive launch and/orlanding areas) or encompass particularly sensitive components of thespacecraft (e.g., navigational components, power supply, etc.).Moreover, each of the first three panels 16, 18, 20 also has a uniformresolution in the example shown. A fourth panel 22, on the other hand,might have a non-uniform resolution, which may be used to target evensmaller areas for heightened detection sensitivity. In one example,traces are 0.020-inches thick and separated from each other by 0.020inches.

FIGS. 3A and 3B illustrate a multi-dimensional detection system 24,wherein the system 24 generally includes a multi-layered panel assembly26 with a sensing panel 57 that is powered by a power supply 28 andcommunicatively coupled to a monitor 30. In some embodiments the monitor30 may be a computer monitoring device that can only receive commandsand/or data. In other embodiments the monitor 30 may be a computermonitoring device that can send and receive commands and/or data. And infurther embodiments the monitor 30 may be a microcontroller ormicroprocessor embedded within the multi-layered panel assembly 26.Wherein the damage detection data may be stored within themicrocontroller or microprocessor for accessing at a later date foreventual download and viewing on an external device.

In one example, an organic inherently conductive polymer may be used asa damage detection layer. For example, polyaniline derivatives have beendemonstrated to function well as a damage detection conductor in athin-film coating configuration having several thicknesses. Moreover,polyaniline coatings on polyethylenephthalate (PET) and KAPTON-H haveperformed successfully for damage detection. In addition to polyaniline,carbon nanotube (CNT), metal nanoparticle inks, and combinationsthereof, thin films produced in accordance with embodiments of thepresent invention may be employed as conductors in thin-filmconfigurations.

In the illustrated multi-dimensional detection system 24,two-dimensional detection layers of thin film may be used to form alayered composite, with thicker, non-detection layers separating thedetection layers from one another. The thin-film detection layers can beformed of materials having a conductive grid or striped pattern such asthe pattern 14 (FIG. 2) already discussed. The conductive pattern may beapplied by a variety of methods including, but not limited to, printing,plating, sputtering, solvent casting, photolithography, and etching.

In a preferred embodiment, thin, conductive patterns are printed on oneor more of a wide variety of substrates using a standard inkjet printerwith several conductive inks. The substrates include, but are notlimited to, polyimides, fluoropolymers, vinyl polymers, cotton fabrics,paper, and NOMEX. In designing the detection system, the number ofdetection layers chosen may depend on the level of damage detectiondetail needed. The damage will result in a change in electricalproperties in the grid of conductive traces which can be detectedutilizing the monitor 30, which may comprise a time domainreflectometer, resistivity monitoring hardware, capacitive measurementcomponents, or other resistance-based detection systems. Moreparticularly, the multi-dimensional damage detection system 24 caninclude a multiplicity of non-detection layers separated from oneanother by a multiplicity of detection layers, with each of thedetection layers being connected to the monitor 30 in order to providedetails regarding the physical health of each individual detectionlayer. If damage occurs to any of the detection layers, a change in theelectrical properties of the damaged detection layer(s) may also occur,and a response may be generated. For example, real-time analysis of theresponses may provide details regarding the depth and location of thedamage. Moreover, multiple damage locations can be detected, and theextent (e.g., depth) of each damaged area can result in the generationof prognostic information related to the expected lifetime of thelayered composite system.

The illustrated detection system 24 can be easily fabricated usingcommercial off-the-shelf (COTS) equipment and the detection algorithmsmay be updated as needed to provide the level of detail needed based onthe system being monitored. Connecting the monitor 30 to the thin-filmdetection layers of the panel assembly 26 may provide a method ofmonitoring any damage that may occur.

For example, the monitor 30 can systematically output a test signal tothe panel assembly 26 and manipulate the input data to determine aconclusion, wherein damaged trace/line and defect line numbers may besorted in ascending order and then grouped into individual data arraysaccording to layer. The arrays may also be normalized so that each linenumber is referenced from a particular range (e.g., 0-167). Once thedamaged and defect line numbers have been normalized, the monitor 30 maycalculate the damaged line-number-to-line-number spacing. Damaged linenumbers that occur sequentially can be grouped together to form a damagezone. The damage zone size may be calculated by determining the numberof sequential lines found.

Once the damage zone size is calculated, the monitor 30 may resolve theappropriate defect analysis state to execute. In order to resolve theexecution state, the monitor 30 may assume that the damage occurs on thepanel assembly top (i.e., outer) layer and traverses through eachsubsequent layer. If damage does not occur on the top layer first, butrather on the inner layers only, the monitor 30 may reject and notprocess the data.

In one example, the monitor 30 utilizes a state machine with fivestates, wherein each state represents the number of layers of damagedetected plus an idle state. The damage occurs in the proper order forthe correct state to be performed. For example, if the embeddedmonitoring system reports that damage occurred on only the top layer andthe bottom layer, then the state performed is State 1. In such a case,the data from the bottom layer may be ignored.

State 0—Idle, default, no data is processed

State 1—Damage detected on top layer only

State 2—Damage detected on the top two layers (1 & 2)

State 3—Damage detected on the top three layers (1, 2, & 3)

State 4—Damage detected on all four layers

Damage detected on the top layer only may be the easiest to process. Insuch a case, the monitor 30 can calculate the x-coordinate based on thenormalized damaged line number multiplied by the spatial resolution ofthe grid (e.g., 0.04 inches). The y-coordinate may be set to zerobecause it is unknown since the damage did not penetrate to the secondlayer. The monitor 30 may complete its operation by populating a damageattributes cluster array. When the software detects that they-coordinate is equal to zero in the cluster array, it can automaticallydraw a vertical color-coded line on the chart display object.

If damage is detected on two or more subsequent panel assembly layers,then the monitor 30 may begin a series of operations to determine theappropriate generalized scenario for each state. There are numerouslower-level cases that occur in each generalized scenario.

The following scenarios might be calculated for States 2-4.

Scenario #1: Damage Zone Array Sizes Equal 1

Since one damage zone is detected, the monitor 30 may pair the layer onedamaged line numbers (x-coordinates) to the layer two damaged linenumbers (y-coordinates) to form a coordinate pair. Since the damagedline numbers are sorted in ascending order, the lowest-value damagedline number in layer one (x) is paired to the lowest-value damaged linenumber in layer two (y). If the damage is symmetrical, the operator willobserve on the chart graphic display object resolved color-coded pointscorresponding to damage depth layer; otherwise, whichever direction thenumber of damaged lines is greater (x or y) then vertical or horizontallines will appear to represent the extra broken sensing lines that couldnot be paired. The monitor 30 can complete its operation by populatingthe damaged attributes cluster array.

Scenario #2: Damage Zone Array Sizes Are Equal but Greater Than 1

This scenario may occur for two reasons. First, multiple damage zonescould be detected, which might happen when damage occurs simultaneouslyat different spots on the panel assembly (i.e., micrometeoroid shower).The second reason has to do with known defect lines. Damaged linenumbers that occur sequentially are grouped together to form a damagezone. A single damage zone can appear to be multiple damage zones ifthere are defect lines that occur between a damaged line numbersequence, causing the pattern to not be sequential. In this case, themonitor 30 determines if there are defects found in the zone, and if so,the damage zone size may be incremented based on the number of defectsfound. The monitor 30 can complete its operation by populating thedamaged attributes cluster array.

Scenario #3: Damage Zone Array Sizes Are NOT Equal

This scenario may occur for two reasons. First, multiple damage zonesmay be detected, which can happen when damage occurs simultaneously atdifferent spots on the panel assembly (e.g., micrometeoroid shower). Inthis particular scenario though, multiple damage zones may have beendetected on the top layer, while on layer two, there were fewer damagezones detected because all the damage detected on the top layer didn'tpenetrate evenly through the panel assembly. Therefore, the damage zonearray sizes might not be equal. If this is the reason, then the damagedline numbers from each layer might not be resolvable because there maybe insufficient information to say for certain the location. Therefore,color-coded vertical and/or horizontal lines could be drawn to representthe broken sensing lines. In such a case, the operator may generallyknow the damage area, but not necessarily the exact location.

The second reason has to do with known defect lines (e.g., tracecontinuity signature information). Damaged line numbers that occursequentially can be grouped together to form a damage zone, as alreadydiscussed. A single damage zone can appear to be multiple damage zonesif there are defect lines that occur between a damaged line numbersequence, causing the pattern not to be sequential. In this case, themonitor 30 may determine if there are defects found in the zone, and ifso, the damage zone size can be incremented based on the number ofdefects found. There is a special scenario for the defects case. If twodamage zones occurred simultaneously and one of those zones penetratedan area containing known defect traces and the other zone didn't containknown defect traces, the monitor 30 may have sufficient information toresolve the damage location and assign the appropriate x- andy-coordinates. If two damage zones exist and both have known defecttraces or more than two damage zones exist, the algorithm may be unableto resolve the location and color-coded vertical and/or horizontal linescan be drawn to represent the broken sensing lines. Again, the monitor30 may complete its operation by populating the damaged attributescluster array.

After the generalized scenarios have been executed and the damagedattributes cluster array have been populated with the most currentinformation, the illustrated monitor 30 plots the damaged attributescluster array data on a graphic chart display object. If either x- ory-coordinate pair equals 0, then a color-coded vertical or horizontalline may be plotted rather than a point, wherein the line or point fillcolor may be determined by a damage depth layer value in the damagedattributes cluster array. For example, the layer damage color code couldbe defined as below.

Top Layer=white

Second Layer=blue

Third Layer=yellow

Bottom Layer=red

In the illustrated example, a first plurality of inside conductive pads34 facilitate electrical connection to the conductive traces (e.g.,horizontally arranged) of a first detection layer, and a secondplurality of inside conductive pads 32 facilitate electrical connectionto the conductive traces (vertically arranged) of a second detectionlayer. Where inside conductive pads 32 and 34 may be configuredperpendicular to each other. Similarly, a first plurality of outsideconductive pads 38 may facilitate electrical connection to theconductive traces (horizontally arranged) of a third detection layer,and a second plurality of outside conductive pads 36 can facilitateelectrical connection to the conductive traces (vertically arranged) ofa fourth detection layer. Where outside conductive pads 36 and 38 may beconfigured perpendicular to each other. The inside conductive pads 32,34 and the outside conductive pads 36, 38, which may be disposed on acircuit substrate 56 adjacent to the perimeter of the panel assembly 26,can be used to interconnect panels with one another or to connect panelsto the monitor 30. Indeed, the monitor 30 may be coupled to the grid ofconductive traces via a wireless link (e.g., Bluetooth or Wi-Fi) or awired link, and may even be embedded into the panel assembly 26 itself.In one example, such an embedded monitoring system is capable ofmonitoring the health of hundreds of sensing lines and reporting theirstatus within seconds. Moreover, conductive traces of successivedetection layers may be arranged substantially perpendicular to oneanother in order to achieve the desired detection grid, as alreadydiscussed.

Thus, a total of 28 data traces/lines from a microcontroller of themonitor 30 might be used to inject test signals into the parallelconductors in the detection layers, and a total of 24 data lines may beused to monitor the presence of the test signals at the opposite ends. Aseries of diodes 39 can also used to isolate the lines in the detectionlayers from each other in order to be able to evaluate the condition ofeach line independently of the condition of other lines. The test signalmay be composed of a sequence of digital ones and zeros (e.g., binarypattern) and can be applied to one end of each line, wherein the signalat the opposite end may be monitored to determine the presence orabsence of the test signal.

The monitor 30 at the end of each line may expect to see the binarypattern in order to make a determination that the integrity of the lineunder test has not been compromised, wherein deviations from theexpected pattern may indicate that damage has occurred. In one example,a connection may be made at the cathode of each isolation diode 39downstream from the monitor 30. If the peak voltage is above thecomplementary metal oxide semiconductor (CMOS) logic threshold levelthat signifies a digital “high” or “one,” the trace may be considered agood (i.e., undamaged) line. Such an approach can enable detection ofdamaged lines that are not completely broken (e.g., have a resistancethat is high enough to drop the voltage level below the logicthreshold). Once a failure has been detected, the line numberinformation may be stored in non-volatile memory to allow for it to beused as a baseline of information related to existing damage. Thenon-volatile flash memory can provide the capability to store hundreds(e.g., 256) of broken lines or damage identifier (ID) information. Themaximum historical data that can be stored may be based on a 5-bitdamage ID number and a 10-bit damage line number value. Storing theinformation in this format may be very efficient and can involve arelatively small memory footprint.

FIG. 4 shows a sectional view of a detection panel 40 having a pluralityof detection layers 42 separated from one another by one or morenon-detection layers 44. In particular, each detection layer 42 mayinclude a film substrate and a plurality of conductive traces coupled tothe film substrate, as already discussed. Moreover, the conductivetraces of successive detection layers can be substantially perpendicularto one another in either a uniform or non-uniformresolution/configuration. In the illustrated example, adhesive layers 46are used as an interface between successive detection and non-detectionlayers. A circuit substrate 48 may also be coupled to an outside layerof the panel 40, wherein the circuit substrate 48 may be constructed ofa flexible and/or rigid material. Of particular note is that a flexiblecircuit substrate 48 may be particularly advantageous for inflatableplatform structure applications.

FIG. 5 illustrates a sectional view of the aforementioned detectionpanel assembly 26, wherein the illustrated detection panel assembly 26has a panel with a staggered profile to enhance connectivity. In theillustrated example, a plurality of detection layers 52 (52 a-52 d) areseparated from one another by a plurality of non-detection layers 54.The horizontally arranged conductive traces of the bottom (e.g., first)detection layer 52 a can be connected to one or more inside conductivepads 34, whereas the vertically arranged (into the page) conductivetraces of the next (e.g., second) detection layer 52 b may be connectedto one or more inside conductive pads 32 (FIG. 3B). Similarly, thehorizontally arranged conductive traces of the next (e.g., third)detection layer 52 c can be connected to one or more outside conductivepads 38, whereas the vertically arranged (into the page) conductivetraces of the top (e.g., fourth) detection layer 52 d may be connectedto one or more outside conductive pads 36 (FIG. 3B). The conductivetraces of the upper set of detection layers 52 c, 52 d, may have a widerprofile in order to provide greater clearance and facilitate connectionto the outside conductive pads 38, 36, respectively. The illustratedconductive pads 34, 38 are mounted to a circuit substrate 56, which isalso coupled to an outside layer of the panel assembly 26, in theexample shown.

To ensure good electrical continuity between the flexible sensing paneland the printed circuit board 56, a mounting frame (or compression ring,not shown) may be used to apply even compression and proper alignment ofthe sensing panel to the circuit board 56. Alignment dowels can beincluded in the printed circuit board assembly, wherein the flexiblesensing panels may have corresponding holes that enable proper alignmentand prevents panel slippage. In one example, the compression ring ismade of polycarbonate and has a 6-inch by 6-inch opening in the centerto allow the active area of the sensing panel to be fully exposed. Thecompression ring may attach to a back plate behind the circuit boardwith screws. The screws can pass through holes in the compression ring,one at each corner and three along each side, and corresponding holes inthe circuit board, then thread into helicoils in the back plate. Whenthe screws are tightened, the ring can bias/press the sensing panelagainst the circuit board 56 and secure it in place.

On the bottom side of the compression ring, covering the portion of thecircuit board which has the pads, there may be a gasket (e.g.,buna-n-rubber). The gasket provides a tight fit against the sensingpanel that both ensures good contact and keeps the circuit board 56 andother components from being exposed to the elements.

FIG. 6 shows a flexible panel assembly 27. The illustrated panelassembly 27 includes a multilayered flexible panel 29 coupled to aflexible circuit board 31. The panel assembly 27 may also include amicrocontroller, custom firmware, bidirectional serial port driver, anddiodes for electrical isolation. In addition, the panel assembly 27could include wired/wireless network capability or the entire assembly27 could be fabricated from a rigid-flexible printed circuit board.

FIG. 7 shows a method 58 of evaluating a structure. The method 58 may beimplemented as hardware, firmware, software (e.g., LabVIEW), or anycombination thereof, in a monitor such as the monitor 30 (FIG. 3A),already discussed. Illustrated processing block 60 provides forselectively deactivating one or more of a plurality of detection layersor sensing lines in a plurality of interconnected panels based on adepth detection parameter. For example, block 60 could involvedeactivating (e.g., masking) the conductive traces of the firstdetection layer 52 a (FIG. 5) so that damage to only approximately threefourths of the overall thickness of a given panel would be detected. Anelectrical property change with respect to the activated detectionlayers may be detected at block 62, wherein block 64 can generate one ormore of a diagnostic output and a prognostic output based on theelectrical property change. In one example, a graphical user interface(GUI, e.g., written in LabVIEW) is used to communicate the detectionresults to various personnel via the monitor 30 (FIG. 3A).

FIG. 8 shows a method 59 of detecting damage in greater detail.Illustrated processing block 61 provides for initialization of localvariables, graph display objects (e.g., X and Y axes; grid), andcommunication settings, wherein a state machine can be invoked at block63. In the illustrated example, the state machine is event driven andsupports up to nine different states. Block 65 may conduct mask switchcontrol in order to remove known defect traces and compare baseline datato current data. A damage detection software algorithm or subroutine maybe invoked at block 67, wherein the damage detection software algorithmor subroutine sorts and normalizes damaged trace identifiers, as well aspairs coordinate values, in the example shown. Blocks 63, 65, and 67 maybe executed in a loop on a periodic basis (e.g., every 100 ms).Illustrated block 69 provides for exiting the program and closingcommunication ports.

Thus, software may interpret the damage line numbers detected by amicrocontroller and sort and organize the individual damaged sensinglines into damage zones with location and depth. In one example, thereare two types of software—GUI software and firmware. The firmware, whichmay be stored in non-volatile memory in the microcontroller, can monitorthe individual sensing lines by sending out a test signal sequentiallyon each line. It may also store historical data regarding the damage IDand damage line numbers and transmit that data to the GUI whenrequested. During normal operation, the microcontroller outputs a testsequence composed of alternating ones and zeros. At the same time, themicrocontroller determines the response of the grid of conductive tracesto the test sequence and determines whether the correct pattern has beenreceived or not. The integrity of a line in the detection layer may bedeemed to be good (i.e., undamaged) if the received pattern is identicalto the transmitted pattern. The process may then be repeated for alltraces. The microcontroller can also be programmed to listen forcommands coming from a host computer. These commands can be used torequest specific functions from the board, including real-time retrievalof data, baselining of existing damages, and auto-loop or single scanmode of operation.

FIG. 9 illustrates a GUI in which panel damage is characterized forusers. In the illustrated example, multiple points 66 (66 a, 66 b) aredrawn against a pattern reflecting a grid of conductive traces, whereinthe points represent collective damage to the traces of the grid (e.g.,a damage zone). The points 66 may be drawn differently to reflect damagedepth (e.g., the deepest layer damaged). For example, the designed point66 a could indicate that damage has been detected down to the thirddeepest layer, whereas the solid point 66 b might indicate that damagehas been detected down to the fourth deepest layer. In such a case, theuser may be able to readily ascertain an angle of incidence to theimpacted panel as well as the level of severity. Other differentiatorssuch as color and/or size may also be used for the points 66. Moreover,the points 66 can be used to determine damage area.

Additionally, the GUI may be used to indicate particular traces thathave been damaged (e.g., where damage pinpointing is not available). Inthe illustrated example, a vertical line 68 is drawn to reflect damageto a vertically arranged trace, and a horizontal line 70 is drawn toreflect damage to a horizontally arranged trace. The lines 68, 70 mayalso be drawn differently to reflect damage depth. For example, the dashfrequency of the vertical line 68 could indicate that damage occurred inthe second deepest layer, whereas the dash frequency of the horizontalline could reflect that damage occurred in the shallowest layer. Otherdifferentiators such as color and/or size may also be used for thepoints 66.

Implementation Example

The system can include three main custom designed subsystems: afour-layer KAPTON sensing panel with mounting frame, an embeddedmonitoring system, and a graphical user interface (GUI). The sensingpanel may include four monitoring layers perpendicular to each othercreating a three-dimensional grid pattern. Each layer may include aKAPTON sheet printed with 168 parallel conductive ink traces 20-milswide with a trace-to-trace spacing of 20 mils. KEVLAR fabric can besandwiched between each sheet and glued together with adhesive to formthe sensing panel. A mounting frame can align and mount the sensingpanel to the embedded monitoring system.

The system may determine the identification number of the sensing panelby utilizing either the first four or the last four conductive traces oneach of the individual layers. This is accomplished by creating knownpatterns of breaks in the electrical continuity of these traces andscanning the traces for continuity. For example, if the first fourtraces of a layer are used (4 bits), up to 16 different combinations(e.g., trace continuity signatures) can be generated, providing thecapability to identify up to 16 unique panels. Additional conductivetraces can be utilized on the other layers to increase the total numberof unique panels that can be identified.

The embedded monitoring system may include a printed circuit board thatinterfaces with the sensing panel. Additionally, a microcontroller ormicroprocessor may actively monitor the health of all 672 traces (4×168)and report status information to the GUI software. Flash memory can beused to store an ID and the damaged line numbers associated with each IDnumber. The on-board memory may be used to log historical data, thusallowing the reconstruction of the damage events at a later date.Knowledge of the sequence of damage events and which sensing lines werebroken for each event can enable the GUI software to sort and accuratelyassign a damage location. The microcontroller status may be wirelessly(e.g., up to 100 meters) reported to a laptop running the GUI, whereinthe GUI software may be written in LabVIEW and can use a customdeveloped damage detection algorithm to determine the damage locationbased on the sequence of broken sensing lines. The algorithm mayestimate the damage size and maximum depth, and also plot the damagelocation on a graph to be viewed on a computer monitor or other graphicsdevice.

The GUI software may utilize scripting to enable either autonomous ormanual operation of the system. This allows for a single GUI to beutilized for multiple operational scenarios, making the system moreversatile. Script files may contain other information related tooperational mode (autonomous or manual), data sampling rate, time stamp,method of data transmission (e.g., wireless, Bluetooth, serial,Ethernet, Wi-Fi, etc.), and operational tasks (e.g., read baseline,determine panel identification number, load mask file, erase baseline,etc.). The script file can be modified and specifically tailored, asneeded, to provide the most efficient operation of the system for agiven application.

Integrated testing included drilling holes of various diameters, shapes,and sizes at different depths into the sensing panel and verifying thefunctionality of both the embedded systems and the GUI software. Theholes emulated the potential damage which can be caused bymicrometeorites or other space debris impacting the habitat's exteriorsurface.

Preferred embodiments may therefore include an apparatus having a panelwith a plurality of detection layers separated from one another by oneor more non-detection layers, wherein the plurality of detection layersform a grid of conductive traces. The apparatus can also have a monitorcoupled to the grid of conductive traces, wherein the monitor isconfigured to detect damage to the pane in response to an electricalproperty change with respect to one or more of the conductive traces.

Other preferred embodiments may also include a system having a platformsuch as an inflatable spacecraft or non-inflatable habitation structurewith a plurality of interconnected panels, wherein each panel has aplurality of detection layers separated from one another by one or morenon-detection layers. The plurality of detection layers may form a gridof conductive traces. The system can also have a monitor coupled to eachgrid of conductive traces, wherein the monitor is configured to detectdamage to the plurality of interconnected panels in response to anelectrical property change with respect to one or more of the conductivetraces.

Embodiments may also include a method in which a test signal istransmitted to a plurality of interconnected panels, wherein each panelhas a plurality of detection layers that form a grid of conductivetraces. The method can also provide for identifying one or more damagezones in the plurality of interconnected panels based on a response ofthe grid of conductive traces to the test signal and trace continuitysignature information associated with the plurality of interconnectedpanels.

Moreover, embodiments can include a computer readable storage mediumhaving a set of instructions which, if executed by a processor, cause acomputer to transmit a test signal to a plurality of interconnectedpanels, wherein each panel has a plurality of detection layers that forma grid of conductive traces. The instructions, if executed, may alsocause a computer to identify one or more damage zones in the pluralityof interconnected panels based on a response of the grid of conductivetraces to the test signal and trace continuity signature informationassociated with the plurality of interconnected panels.

Additionally, embodiments may include a method of fabricating aninflatable spacecraft or habitation in which a plurality of panels areprovided as an exterior structure of the inflatable spacecraft. Eachpanel can have a plurality of detection layers separated from oneanother by one or more non-detection layers, wherein each detectionlayer includes a film substrate and a plurality of conductive tracescoupled to the film substrate. Moreover, conductive traces of successivedetection layers may be substantially perpendicular to one another,wherein the plurality of detection layers form a grid of conductivetraces. The method can also involve interconnecting the plurality ofpanels, and configuring a monitor to selectively deactivate (e.g., mask)one or more of the plurality of detection layers or sensing lines basedon a depth detection parameter. The monitor may also be configured todetect damage to the plurality of panels in response to an electricalproperty change with respect to one or more of the conductive traces,and generate one or more of a diagnostic output and a prognostic outputbased on the electrical property change. In addition, the method mayinclude coupling the monitor to the plurality of panels.

Thus, embodiments of the present invention can provide a uniquemulti-dimensional damage detection system that is completely flexibleand can easily be designed to gather as much or as little information asthe end user deems necessary. Additionally, individual detection layerscan be turned on or off as needed and the controlling algorithms may beoptimized as needed. Simply put, the illustrated systems can be used togenerate both diagnostic and prognostic information related to thehealth of layered composite structures, which may be essential if suchsystems are utilized for space exploration and habitat.

The term “coupled” may be used herein to refer to any type ofrelationship, direct or indirect, between the components in question,and may apply to electrical, mechanical, fluid, optical,electromagnetic, electromechanical, or other connections. In addition,the terms “first,” “second,” etc. may be used herein only to facilitatediscussion, and carry no particular temporal or chronologicalsignificance unless otherwise indicated.

Those of ordinary skill in the art will appreciate from the foregoingdescription that the broad techniques of the embodiments of the presentinvention can be implemented in a variety of forms. Therefore, while theembodiments of this invention have been described in connection withparticular examples thereof, the true scope of the embodiments of theinvention should not be so limited since other modifications will becomeapparent to the skilled practitioner upon a study of the drawings,specification, and following claims.

We claim:
 1. A system comprising: a platform structure including aplurality of interconnected panels, wherein each panel has a pluralityof detection layers separated from one another by one or morenon-detection layers, and wherein the plurality of detection layers forma grid of conductive traces and wherein each detection layer includesone or more known defect traces, and wherein the panel has a tracecontinuity signature that is defined by the known defect traces of thedetection layers in the panel; and a monitor coupled to each grid ofconductive traces, wherein the monitor is configured to detect damage tothe plurality of interconnected panels in response to an electricalproperty change with respect to one or more of the conductive traces. 2.The system of claim 1, wherein each detection layer includes a substrateand a plurality of conductive traces coupled to the substrate.
 3. Thesystem of claim 2, wherein conductive traces of successive detectionlayers are substantially perpendicular to one another.
 4. The system ofclaim 1, wherein the grids have a non-uniform resolution.
 5. The systemof claim 1, wherein the monitor is configured to selectively deactivateone or more of the plurality of detection layers or sensing lines basedon a depth detection parameter.
 6. The system of claim 1, wherein themonitor is configured to generate one or more of a diagnostic output anda prognostic output based on the electrical property change.
 7. Thesystem of claim 1, further including a circuit substrate coupled to anoutside layer of each panel.
 8. The system of claim 7, wherein thecircuit substrate includes a plurality of inside conductive pads and aplurality of outside conductive pads disposed adjacent to a perimeter ofeach panel, and wherein the plurality of inside conductive pads and theplurality of outside conductive pads are electrically connected to agrid of conductive traces corresponding to each panel.
 9. The system ofclaim 1, wherein each detection layer includes a plurality of knowndefect traces, and wherein each panel has a trace continuity signaturethat is defined by the known defect traces of the detection layers inthe panel.